Method and apparatus for refrigerating with solid refrigerants



Demo 31, 1935. 1 w. e. MAYER 2&265'553 METHOD AND APPARATUS FORREFRIGERATING WITH SOLID REFRIGERANTS Filed June 9, 1932 5 Sheets-Sheet1 emu-noon 0000a WWNEESES INVENTOR 3% $6M. A g m, aflzw w' Dec. 31,1935. w G MAYER 2,026,353

I METHOD AND APPARATUS FOR REFRIGERATING WITH SOLID REFRIGERANTS FiledJune 9, 1932 5 Sheets-Sheet 2 WITNESSES Dec. 31, 1935. w. e. MAYER2,026,353

METHOD AND APPARATUS FOR REFRIG-ERATING WITH SOLID REFRIGERANTS.

Filed June 9, 1952 3 Sheets-Sheet 3 R O T N E v m h fi a 0 a 7 e. 6 4

' wn'nsssts ifiQM ideal refrigerant,

Patented Dec. 31, 1935 UNITED STATES] PATE NT] OFFICE I A'rmewun SOLIDnnmreaaanrs William G. Mayer, Pittsburgh, Pa. Application June 9, 1932,Serial No. mass 5, Claims.

This invention relates to refrigeration, and particularly to therefrigeration of vehicles by means of solid carbon dioxide. 4

Ordinary water ice as a refrigerant for vehicles, such as trucks,carrying perishable materials, e. g. foodstuffs, is not satisfactory forvarious reasons. Chief arn ong these are the bulk and weight of ice andb rme which must be carried, and the rather limited cooling effect andrefrigeration period available.- Also, the refrigerating effect is quiterestricted.

The advantages of solid carbon dioxide, e. g., in the form of so-calledsnow or ice, are well known. Its temperature is about ll5 F., and itdoes not melt, but sublimes. It thus provides greater refrigeratingpossibilities than water ice,

A further object is to provide an apparatus for refrigerating with solidcarbon dioxide, which is I compact, of sturdy and inexpensiveconstruction,

eflicient in operation, adapted for the practice of v the methodembodied in the invention, and which in a particular embodimenteliminates contact of ing partition of metal 'of high'thermalconductivity to solid carbon dioxide refrigerant in heatexchangingcontact with the other side of the partition. Most suitably thepartition consti-, tutes a wall of a container enclosing the refrigandit eliminates the collection of liquid with'its erant, and its exteriorpresents td the chamber attendant disadvantages. In general 1 pound ofsolid carbon dioxide is capable of the same refrigerating efi'ect asabout 15 pounds of water ice. Thus lower temperatures, with betterpreserva tion of foodstuffs, are possible, and pay loads and routelengths may be increased. Furthermore, solid carbon dioxide does notrequire the brines needed with water ice, so that this source of non-payweight, and the corrosion due to brine, are eliminated. v Theseproperties render solid carbon dioxide an particularly for vehiculartransportation of perishables. However, it is substantially moreexpensive weight-for-weight than water ice; gaseous carbon dioxideformed on evaporation may exert an injurious effect on some foods; andits u'serequires some measure of temperature control, since otherwisefoods refrigerated with it may be frozen; Therefore, trucks and similarvehicles using'carbon dioxide refrigerant must be adapted to preventundue evaporation of the carbon dioxide and contact of the gas with itsload, as well as providing for temperature control. The constructions,whether vehicular or stationary, available. heretofore have not ciency'of refrigeration because the cool gas is retained for further heatabsorption. The refrigerating efllciency may be, and preferably is,further increased by relieving the excess CO2 gas into the insulation ofthe enclosing walls of the refrigerated chamber. In circulating throughthe insulation the gas absorbs further amounts of heat, so that itapproaches atmospheric temperature before finally reaching theatmosphere.

This aflords utilization of substantially the entire capability of thecarbon dioxide to absorb heat; furthermore the transfer of heat from thefrigerated chamber is minimized.

, atmosphere through the enclosing walls of the re- The invention isfurther predicated upon my I discovery" that by restrlcting the heattransfer substantially to the partition, or wall, with which therefrigerant is in contact, evaporation of the refrigerant will beconfined primarily to the face in contact with the container wall, sothat the refrigerant will continuously present substansuit particularneeds, which utilizes the major tially constant refrigerating area. Thisaffords proportion of the heat absorbing capacity of the refrigerantmaterial, is economical, applicable constancy of heat transfer, withconsequent uniformity of refrigerating effect and improved efliciency.Also in accordance with the invention regulation of the rate of heattransfer between,

I the chamber and the refrigerant to maintain the chamber at a desiredtemperature, is accomplished by interposing resistance to thermalconduction between the refrigerant and the heat exchanging partition.

The apparatus embodied in the invention comprises a chamber forcontaining the materials to berefrigerated, preferably one having itsenclosing walls insulated with a material permeable by gas. Therefrigerant is enclosed within a container havinga heatexchangingsurface of metal of high thermal conductivity exposed to thechamber, and advantageously the container is associated with the top, orroof, of the chamber, with its bottom supporting the refrig-. erant.Preferably the container is provided externally with a large heatexchanging surface, as by providing it with a plurality of fins or ribs.For most purposes the container is constructed to 1 prevent leakage ofsubstantial amounts of gaseous carbon dioxide into the chamber, and mostsuitably to maintain the evaporated CO2 gas under pressure, means beingprovided to relieve excess gas according to circumstances.

, Although the exposed wallsof the container may act together as a heatexchanging partition, it is preferred, for reasons presently to beexplained, to so construct the container as to restrict the heattransfer substantially to the heat exchanging partition, e. g. thebottom wall. In such case the remaining exposed walls are insulated fromthe refrigerant,,but most advantageously they act to assist in absorbingheat from the container, and to transfer it to-the heat exchanging wall.

The invention is particularly adapted for use with trucks and othervehicles and for purposes of further illustration will be so described,although it will be understood that it is not restricted thereto and maybe applied to other uses.

In the accompanying drawings Fig. 1 is a fragmentary side elevation,partly in section, of a truck body showing one embodiment of theinvention; Fig. 2 an enlarged horizontal view, partly in section, of therefrigerant container taken on line 11-11, Fig. 1; Fig. 3 a perspectiveview of the container shown in Figs. 1 and 2; Fig. 4 a perspective viewof an insulating pad for use in the practice of the invention; Fig. 5 abottom plan view of another form of refrigerant container illustratingthe preferred embodiment of the inbetween walls 2 is filled withsuitable heat ins'ulating material 4, preferably one permeable by gas,such as the fibrous insulators now commonly used for instance Kapok orBalsa wool), As shown in Fig. 1, a refrigerant container 5 is mountedinahatchway formed in the roof of the truck body. Container 5 comprises abase plate 5, which supports a cake I of solid carbon dioxide withinthe-container, and which is connected to vertically positioned sideplates 8.

Plates 6 and 8 are formed from a metal of good thermal conductivity,such as aluminum or its light alloys. dimensions of the container aresuch as to accom- Advantageously the cross sectional modate the standardcakes of solid carbon dioxide, or multiples or uniform fractionsthereof. The container is suspended from the side walls 9 of thehatchway, and in the embodiment shown the container is constructed andis fitted 5 into the hatchwaysnugly to prevent leakage of substantialamounts of ,gas into the compartment.-

Base plate 6 is preferably provided with means for increasing its normalheat radiating capacity, and this may be accomplished by connecting toone or both sides of the base plate sheet metal corrugated to formV-shaped fins. As shown in Figs. 1 and 2, the lower side of the baseplate is provided with corrugated sheets ll forming ribs which extendentirely across the lower side of the base plate, the latter extendinglaterally from the sides 8 toincrease the heat-exchanging surface. Thelateral projections of plate 6 are provided' on the upperv surface withsimilar corru- 20 gated sheets l2, as shown particularly in Fig. 2. Thisconstruction provides channels for circulation of air over the heatradiating surfaces, so as to increase the rate of heat transfer. Suchair circulation may be increased by perforating 25 corrugated sheets IIand I! as at l3 and by cutting slots l4 through the sheets and plate 6.

The construction thus provided is adapted to efiiciently refrigerate thecompartment. In most instances regulation of temperature is desirable,30

, mize CO2 consumption. Such control may be effected by verticaladjustment of the container 35 in the hatchway, or of the refrigerant inthe container, or both. The containerposition may be adjusted by movingit up or down in the hatchway, a plurality of horizontal rows of screwholes l5, Fig. 3, beingprovided in walls 8for 40 that purpose.

Further control of rate of heat, transfer is afforded byinterposing'thermal resistance under the refrigerant. The pad shown inFig. 4 forms a particularly suitable means of doing this. It comprises ahollow box-like structure I 6 formed of metal,the interior beingreinforced by corrugated sheet metal II to resist crushing of the wallsby the refrigerant cakes.- The heat insu-.- lating eifect may beincreased by making the box gas tight to provide dead air space. Beingformed:from-metal and being in full contact with cake I such pads afforddirect heat transferring contact between the refrigerant and base plate6, while they reduce the rate of heat transfer.

I- have found that.p'articular advantages attend the retention underpressure in the container of the gaseous CO2 which is formed as thesolid refrigerant evaporates in absorbing heat from the compartment. Tothis end the container and its associated parts are constructed tomaintain 'the gas under a desiredpressure. For this purpose hatchwaycover i0 is maintained by any suitable means in gas-tight relationshipwith the hatchway. For example to each side of the cover there isconnected 2. spring latch [8 which engages a catch I! mounted on sidewall 9. The latches press the cover against a gasket 20 interposedbetween the cover and the top of the hatchway.

Excess pressure is relieved through an outwardly opening adjustablerelief valve indicated schematically at 2|, a number of types of whichare available. Because the CO: gas formed in the container is quite coldit is preferred to relieve it into insulation 4, soas to obtainadditional refrigerating effect. Thus valve 2| opens into the insulationspace between side walls 2 so that-the gas circulates through insulation4, thus cooling the compartment walls and minimizing heat transfer to.the chamber from the atmosphere. In order to permit free circulationthrough the insulation body structural members, such as indicated at 22,are provided with holes 23 as need be. The gas finally escapesto theatmosphere through the cracks in the body walls.

The refrigerating unit thus provided possesses numerous advantages,among which are its compactness, the slight weight of the container andrefrigerant needed to equal the refrigerating effect of large volumesand weights of water ice, and the ability to prevent contact offoodstuffs with gaseous CO2. y

Especially great advantages flow from the effi- "ciency of the unit,which arises from a number of factors. In the first place, the, heattransfer is directly from the chamber through the heat exchanging wallto the refrigerant. This is augmented by presenting a large heatabsorbing surface to the chamber, and by having the refrigerant cake infull contact with the other side of the exchanging wall, 1. e. having aflat surface of refrigerant entirely contacting the plane surfaced base.I

Further efficiency is derived from the ability to regulate the rate ofheat transfer, so that the refrigerant .is not used needlessly, and sothat therefrigeration is optimum for the particular materials beingcooled. i Thus if the heat exchanging surface is too great for therefrigeration-desired, the container may be moved heat transfer, andvice versa. A similar result is obtained 'by the use of thermalresistance between the plate and cake 1. described are-especiallydesirable, as they maintain metallic and full contact between the plateand the refrigerant, and merely reduce the rate of heat-transfer to thebase and the area of upwardly in. the hatchway, to reduce the rate' ofrefrigerant exposed to the side walls. Both means of adjustment may beused,. for example to roughly approximate the desired temperature byvarying the container position, and completing the regulation by the.useof pads. Actual tests have shown-that in this manner desiredtemperatures in the range from 40 F. below zero to- 15 F. above zerocan. be maintained satisfactorily;

formation of CO: gas, and this is used in two ways to appreciablyaugment-the refrigerating effect. is available for further absorption ofheat, and it represses evaporation thereof, thus decreasing theconsumption of solid carbon dioxide. In

general, retention of the gas at pressures of from about 5 to 15 poundspersquare inch affords satisfactory results. Second, ancillary coolingis obtained through release of gas to the enclosing'tvalls when thepressure within the container buil'ds'up to a point where it exceeds the.pressure for which the relief valve is set. -The cool gas circulatesthrough the insulation around the enclosing'walls, and this may be, andadt eousl is, enhanced b sealing the linings van ag y y ofIsumciently'to permit brackets 4| to be swung of the inside and outsidewalls, and roof, of the vehicle body, so as to compel the gas toflowover The pads Absorption of heat from'the' chambercauses Byretaining the gas under pressure it and this furtherreduces refrigerantconsump tion, so that substantially the full refrigerating power .of.the CO: is thereby utilized. In addition, this circulation of gasthrough the enclosing walls serves the useful function of keeping the.insulation dry, the-gas flow preventing entry, or at least accumulation,of atmospheric moisture. I

vIn caseinsulation 4 is not;a fibrous or loose and gas permeablematerial, .-'the relief valve may open to the atmosphere, or where meatand the like goods, which are improved, or; whose value is notdeteriorated, by carbon dioxide gas,

are carried the valve-may open directly into the compartment, ifdesired.

The preferred embodiment of the invention is illustrated in Figs. 5 to8, according to which the refrigerant container is ,-mounted whollywithin the chamber to be refrigerated. In this,

embodiment. the container comprises a shell, or 20 box-like structure,advantageously of cast construction, having a base 25, side walls 26,and a top 21. The container is providedwith a-door, for introducingrefrigerant; preferably it forms one end of the container, the oppositeend be- 25 ing closed by a wall 26a continuous with side walls 26. The.container isattached in any suitable manner to the top of the chamber tobe refrigerated, for example by lag screws 210, Fig.

6. Solid carbon dioxide refrigerant Ia rests in 30 complete contact withbottom wall 25, as in the fins, or ribs, 28 and 35 hereinabove, and thedoor is arranged to be 40 gas tight under the pressures used. Variousconstructions may be used for this purpose, but I have found, that, ingeneral, the pressure within the container tends to cause leakage aroundthe periphery ofthe door unless it is of very 45 heavy section, or"unless it is designed to prevent its being sprung by the pressurewithin the container. A door construction which has been found to besatisfactory is illustrated. in Figs. 7 and 8. As 50 there shown thedoor comprises a peripheral flange 3| conforming to the end of thecontainer,

and an integrally. formed body portion 32 which i is bowed outwardly, asseen in Fig. 8. This shape resists'deformation by interior pressure, butto further reinforce it the door isprovided interiorly with longitudinalribs 35.

:The door is hinged to swing at bottom wan 25 of the container byhinge-connections 350; Figs. 5 and 8,.and it, is clamped in closedposition by a cross yoke 36 held pivotally by a pin 3! ma U-b'racket 38integral with and project- 'ing from the face of the door. The door isforced into sealing relationship with a gasket 39 surrounding thecontainer by application of pressure to the ends of yoke 36 throughpressure screws 4|! which move in threadedU-shaped bracket members Ipivotally connected by pins 42 to bosses 43 cast integrally at the sidesof the container. 'To-remove the door, screwsv 40 are backed laterally,thus freeing the yoke andjdoon Prior.

to opening the door the gas pressure is relieved through a hand operatedblow-of! valve 44 pass- [5 ing through a boss formed on one side of thecontainer.

The container just described may be used to effect refrigeration of thechamber within which it is mounted, e. g. a truck body, by transfer ofheat from the chamber through the bottom and side walls of thecontainer, as in the preceding embodiment But where heat is transferredfreely through all sides of the container, as in prior units, the solidrefrigerant diminishes in size in all of its dimensions. This decreasesthe area of contact of the refrigerant with the container wall, and mayresult in decreasing rate of heat transfer. i

In a further aspect of the invention I have found that adequate anduniform refrigeration may be obtained by substantially restricting heattransfer to the wall of the container with which the refrigerant is incontact, which I have found maintains substantially constant contactarea between the refrigerant cake and the heat exchanging partition.This is' accomplished, as shown in perishable materials.

Fig. 6, by mounting an inner liner 45 of wood or other material of lowheat conductivity within the container to form a space between itand theside walls and top. This space is lagged with a heat insulator 46,suclpas cork or the like. The door is likewise. insulated by a panel 460of suitable wood. To increase the area of theheat exchanging surface, toprovide adequate refrigerating effect for all conditions, the sides andends of the container are provided with fins 41 cast integrally with thecontainer. These fins act chiefly to augment the absorption of heat,which they transfer to the base, for the insulation of thetop, side andend walls prevents direct transfer of heat from them to the refrigerant.It is preferred that the total exposed area of the container, i. e. thesurface area of the fins plus the surface area of the walls between thebases of the fins, be at least equal to the area of the roof plus halfthe area of the enclosing walls, as this gives the most satisfactoryresults for most purposes.

It thus appears that in the preferred embodiment fin sides of thecontainer act to absorb heat and transfer it through a single side tothe refrigerant, which is insulated on fin sides, and further that theenclosing walls are refrigerated on fin sides by the evaporated gas.Tests of a refrigerant container constructed in'this manner have shownthat in actual service cake Ia diminishes in size primarily in itshorizontal dimension.

That is, the area of contact with base 25 remains substantiallyconstant, the cake gradually decreasing in height without materiallydiminish ing in horizontal cross sectional area. Thus restriction ofheat transfer substantially to the contact surface maintains asubstantially uniform area of contact between the cake and bottom.

and provides practically constant heat exchanging conditions. v

The retention of CO2 gas under pressure redoor is advantageouslypositioned facing the door of the truck body, so that the refrigerantmay be readily introduced into the container. I

The invention thus provides for adequate and efficient refrigeration ofchambers containing The apparatus provided 5 by the invention and usedin the practice of its method requires but a small amount of space inthe refrigeration compartment. This provides greater refrigeratingspace, and consequently larger pay loads. Furthermore, as the unit isrelatively small, and is preferably constructed from a light metal,lighter trucks can be used, which decreases the initial vehicle cost andits upkeep, and also increases the area of the district that can beserved by a single vehicle. The corrosion due to the use of water ice iseliminated. The refrigeration is improved, being uniform and otherwisemore desirable than that with water ice. Substantial economies attendthe use of evaporated gas in the manner described, because this utilizesas completely as is economically possible the heat absorbing capacity'ofthe refrigerant. Other advantages will be understood by those skilled inthe art.

Actual experience with units embodying the invention has clearlydemonstrated its utility, both in efiecting quick cooling of thechamber,

and maintaining adequate refrigeration, and in providing economy ofrefrigerant. The value of circulating the gas through the enclosingwalls is 3 shown in part by the fact that frost may, and does, appear onthe ceiling and walls for a substantial distance from the unit, orcontainer. This shows the gas to be very cold as it leavesthecontainerfand that this factor substantially 5 reduces the transferof heat'to the chamber from the atmosphere, and that in turn reducessolid CO: consumption.

The invention is not restricted to use with trucks, but is applicable toother vehicles, such as 40 railway or freight cars, and also tostationary refrigeration, as of cabinets and permanent and fixedrefrigerating installations.

This application is a continuation in part of my copending applicationSerial No. 534,721, filed May 4, 1931.

. According to the provisions of the patent statutes, I have explainedthe principle and construction-of my invention and have illustrated anddescribed what I now consider to represent its best embodiment.However,'I desire to have it understood that, within the scope of theappended claims, the invention may be practiced otherwise than asspecifically illustrated and described.

I claim:

1. A bunker for solid carbon dioxide refrigerant comprising a metalliccontainer having top, bottom and side walls of a metal of high thermalconductivity associated in gas-tight relation, said bottom wall beingribbed to provide a total exposed heat exchanging area .at least equalto the area of the roof and one-half the side walls of the chamber to berefrigerated, one of said container walls providing an aperture forintroduction of said carbon dioxide, and a closure for 5 said aperturecomprising an outwardly bowed member, a yoke adapted to press saidmember into gas-tight relation with the sides of the aperture,

and releasable means associated with said container cooperating with theyoke to effect closure. 2. A bunker for solid carbon dioxide refriger--ant comprising a metallic container having top, bottom and side walls ofa metal of high thermal conductivity associated in gas-tight relation,the bottom wall being ribbed to provide a total ex- 15 posed heatexchanging surface equal at least to the area of the roof plus one-halfthe side wall area of the chamber to be refrigerated, one of saidcontainer walls having an aperture for introduction of said carbondioxide, and a closure for said aperture comprising an outwardly bowedplate member, a yoke adapted to press said member into gas-tightrelation with the sides of the aperture, and releasable means associatedwith said container coperating with the yoke to efiect closure, and anoutwardly opening relief valve associated with a wall of said containerfor retaining C02 gas therein under predetermined pressure.

3. A bunker for solid carbon dioxide refrigerant comprising a metalliccontainer having a top wall for association with the roof of the chamberto be refrigerated, a bottom wall and side walls, said walls beingformed of metal of high thermal conductivity associated in gas-tightrelation with one another and one of the side walls providing anaperture for introduction of refrigerant, said side walls beinginteriorly insulated, and a closure for said aperture comprising anoutwardly bowed plate member, a bowed yoke adapted to press said closureinto gas-tight relation with the sides of the aperture, and releasablemeans associated with the container cooperating with the yoke to effectclosure.

4; A bunker for solid carbon dioxide refrigerant comprising a metalliccontainer having a top wall for' association with the roof of the cham-5 ber to be refrigerated, side walls, and a bottom wall ribbedexteriorly to provide a total exposed heat exchanging area at leastequal to the area of the roof plus one-half the area of the side wallsof the chamber to be refrigerated, said container being formed of metalof high thermal conductivity and the walls-being associated in gas-tightrelation with one another with one side wall providing an aperture forintroduction of refrigerant, said container side walls being interiorlyinsu- .lated, and a closure for said aperture comprising an outwardlybowed plate member, a bowed yoke adapted to press said closure intogas-tight relation with the sides of the container, and releasable meansassociated with the container 00- operating with the yoke to efiectclosure.'

5. A bunker for solid carbon dioxide refrigerant according toclaim 4,and an outwardly opening relief valve associated with one of thecontainer walls for retaining C02 gas'therein under predeterminedpressure.

WILLIAM G. MAYER.

